Linewidth-Tolerant Joint Digital Signal Processing for 16QAM Nyquist WDM Superchannel

The performance of Nyquist wavelength division multiplexing (WDM) superchannel, using 16-ary quadrature amplitude modulation (16QAM), is severely degraded due to the existence of inter-channel interference and full-response equalization-enhanced in-band noise. Here, we propose a joint digital signal processing (DSP) technique incorporating digital spectral shaping and maximum likelihood sequence detection for 16QAM Nyquist WDM superchannel with a symbol rate of 28 GBd. Compared with traditional joint DSP, we can obtain 1.8-dB required-OSNR improvement at a bit error rate of 10^-3 for back-to-back measurement. In addition, 0.9-dB peak Q-factor improvement is also secured after 960-km standard single mode fiber transmission. Furthermore, using the proposed joint DSP technique, linewidth tolerance is relaxed from 80 to 230 kHz given 1-dB required-OSNR penalty. Meanwhile, reduction of block-size for carrier phase recovery is also secured, taking 100-kHz linewidth into account.